The subject of the invention is a miniature electromagnetic fuel injector intended for the bulk injection of fuel into the suction pipe of combustion motors. The fuel pressure preferably is in the order of 1-4 bar.
There exist a large number of electromagnetic injection valves for the purpose of fuel injection into the suction pipe of combustion motors. A common characteristic for these injection valves is a desire for high dosage accuracy. Such high dosage accuracies can be achieved only with very short opening and closing times. Opening and closing times for the best known valves are 0.5-1.5 ms, depending somewhat on the impedance of the electromagnet. The required short closing times should be achieved with the lowest possible input of electrical energy.
State of the art valves typically are of axially symmetric design. This armature of such valves is located at the central axis of the valve and acts on a valve obturator which in most cases is of needle-type design. A needle-type valve obturator is a requirement in order to allow for a slender design in the mounting region of the injector. The slender design for the injector is desirable so that the combustion air can pass through the injector region with the least amount of interference. The external diameter of such valves is typically 20-25 mm. The moving mass of needle valves is typically from 2-4 g. In order to prevent objectionable armature bounce, and in order to achieve short floating times, the conventional injectors feature only very small stroke heights. The stroke height of modern injector valves are in the range of 0.05-0.1 mm. In order to prevent unacceptable variations in flow-through characteristics, the state of the art valves require extremely tight machining tolerances. In addition, state of the art valves require a difficult calibration procedure.